I have, both those Polywads (which work as advertised) and some homemade jobs. The homemade ones added about 4" of useable spread at 32 yards to a Full (40 POC) choked 870. Didn't pattern the factory loads.
IMO, the best thing for opening up patterns in old,fixed choke guns that are too tightly choked for modern ammo that one does not want to modify are the Polywads.
Or, seek out Les Greevy's writings on the subject.